<?php
class WP_Map_Iterator extends IteratorIterator {
	function __construct( $iterator, $callback ) {
		$this->callback = $callback;
		parent::__construct( $iterator );
	}

	function current() {
		$original_current = parent::current();
		return call_user_func( $this->callback, $original_current );
	}
}

class WP_Post_IDs_Iterator implements Iterator {
	private $limit = 100;
	private $post_ids;
	private $ids_left;
	private $results = array();

	public function __construct( $post_ids, $limit = null ) {
		$this->db = $GLOBALS['wpdb'];
		$this->post_ids = $post_ids;
		$this->ids_left = $post_ids;
		if ( !is_null( $limit ) ) {
			$this->limit = $limit;
		}
	}

	public function current() {
		return $this->results[$this->index_in_results];
	}

	public function key() {
		return $this->global_index;
	}

	public function next() {
		$this->index_in_results++;
		$this->global_index++;
	}

	public function rewind() {
		$this->results = array();
		$this->global_index = 0;
		$this->index_in_results = 0;
		$this->ids_left = $this->post_ids;
	}

	public function valid() {
		if ( isset( $this->results[$this->index_in_results] ) ) {
			return true;
		}
		if ( empty( $this->ids_left ) ) {
			return false;
		}
		$has_posts = $this->load_next_posts_from_db();
		if ( !$has_posts ) {
			return false;
		}
		$this->index_in_results = 0;
		return true;
	}

	private function load_next_posts_from_db() {
		$next_batch_post_ids = array_splice( $this->ids_left, 0, $this->limit );
		$in_post_ids_sql = _wp_export_build_IN_condition( 'ID', $next_batch_post_ids );
		$this->results = $this->db->get_results( "SELECT * FROM {$this->db->posts} WHERE $in_post_ids_sql" );
		if ( !$this->results ) {
			if ( $this->db->last_error ) {
				throw new WP_Iterator_Exception( 'Database error: ' . $this->db->last_error );
			} else {
				return false;
			}
		}
		return true;
	}
}

class WP_Iterator_Exception extends Exception {
}